The characterization of heterogeneous catalysts by XPS based on geometrical probability 1: Monometallic catalysts

Abstract

Geometrical probability can be used as a basis for the quantification of XPS-signals stemming from random samples such as, for instance, supported heterogeneous catalysts. From a study of three ideal cases, namely extended layers of constant thickness, equally sized spheres and hemispheres on a randomly oriented support, it has been established that the effects of angular and layer thickness averaging are interconnected in such a way that a general model can be derived. It has been found that signal ratios as measured by XPS for convex particles are determined by the surface/volume ratios of the supported phases, nearly independent of particle shape.

Pd characterization by XPS in perovskite catalysts for NOx reduction: influence of thermal aging

“…On the other hand, some discrepancies arise on Pd(AC)/La(R100) which could be explained by the lack of accuracy of the Plyuto and Shpak model [18] because of stronger interactions between Pd and LaFeO 3 . As reported elsewhere, [23] the influence of the morphology of Pd particles depending on the extent of metal/support interactions might also alter the numerical solutions of d Pd . Hence, the stronger metal/support interactions suggested on Pd(AC)/La(R100) might alter the extent of the interface and then the morphology of Pd particles accounting for the presence of spherical and hemispherical particles.…”

“…Based on these considerations, subsequent calculations on the basis of the model developed by Kuipers et al [23] were done on Pd(AC)/La(R100). Nevertheless, numerical solutions did not provide decisive arguments in favor of the stabilization of hemispherical Pd particles which would reflect the occurrence of stronger metal/support interactions on Pd(AC)/La(R100) than on Pd(N)/La(R100).…”

TEM and XPS studies to reveal the presence of cobalt and palladium particles in the inner core of carbon nanofibers

“…The pass energy of the analyzer was set at 70 eV. Calculations to determine the percentage of metal situated on the inner surface of CNF were performed with XPSCAT [32], a dispersion analysis program based on the original idea by Kuipers et al [33,34]. In this model, and based on the TEM images Pd particles were assumed to have hemispherical shapes, whereas for Co particles spherical particles were used.…”

F ischer‐ T ropsch Process

“…The Kerkof-Moulijn [108] and Kuipers models [109] are commonly used for evaluation of nanoparticle sizes from XPS data. These models, however, are only valid for diluted samples (metal content < 10 wt.%).…”